A hierarchical map of science.

<p>We partitioned 7,940 journals connected by 9.2 million citations <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0018209#pone.0018209-Rosvall3" target="_blank">[20]</a> into four major disciplines, which we identified as life sciences, physical sciences, ecology and earth sciences, and social sciences. In physical sciences, we followed a second-level split into the areas of mathematics and of physics and chemistry. The size of the modules represents the fraction of time that a random surfer spends following citations in that field, and the arrows indicate flow volume between the fields. For visual simplicity, we exclude fields and arrows with low flow.